My opinion... NO to legless F9 boosters used to try landing on structures...

Here is how I think this will go down... long term...31 engine BFR boosters will have the necessary bottom thrusters and some sort of deployable landing gear to start with...

Install markers in the landing pad to be able to gauge landing accuracy and repeat-ability after each flight...Fly the rocket and make money... (or just hop a bare booster from launch pad to landing pad if time available)Collect data at landing pad after each flight(measure distances from markers to rocket booster reference points)Improve software and hardware as needed to increase accuracy achieved...

IF and only IF you can get accuracy down to what fins and simple catch slots can handle...THEN you build a catch/launch test fixture* and install it on stilts out near LZ-1 (or somewhere like that)Build one complete booster with the landing fins and normal 31 engines... (no gear like before)Either then do some high altitude hops off the launch pad to the landing fixture as first tests...OR... just go for it and use the booster in the regular rotation of in use hardware...(* fixture simulates proposed replacement launch mount to be installed on launch pad if this works)

Fly the one off Booster in the normal booster rotation till proven out...(note... a crash will not put the entire system down... Just the landing fixture and they will need a new test booster)

Once not in experimental mode...Add more boosters (new or reworks) with fins for landing gear... keep flying and making money...Build and then install a fin catching enabled launch mount on the pad (during an annual range downtime maybe)

THEN... and with maybe 25+ boosters in a row caught on the test fixture at LZ-1 to prove you got this sorted out.Try for the Holy Grail... Launch. Land and Relaunch the same booster in 24 hours off the same pad... (with two different uppers)

Maybe I'm crazy, but the following struck me odd from the IAC 2017 presentation.

Elon was discussing Falcon 9, Falcon 9 having 16 straight successful landings, and is about to move on to Falcon 9 having 30 planned flights next year. Then, at 8:19 in the video, he starts talking about Falcon 9 landing precision, and says, "In fact, we believe the precision at this point is good enough for propulsive landing that we do not need legs for the next version. It will literally land with so much precision it will land back on its launch mounts."

He's talking about Falcon 9. He may have misspoke since BFR was obviously on his mind, but the context says the is saying the next version of Falcon 9 can land on it's launch mounts. BFR is hardly "the next version" when discussing Falcon 9; Block V is.

I'll be the first to say that he MUST have misspoke because that is insane. The risk and additional development it would take to have Falcon 9 land its launch mounts would be insane at this stage in the booster's life. If they were planning to roll this out with Block V we would have seen a test. Also, there is no way you could land without legs on the ship due to the imprecision of the ship, and there is no way in hell that Falcon Heavy boosters could all land on their mounts.

Maybe I'm crazy, but the following struck me odd from the IAC 2017 presentation.

Elon was discussing Falcon 9, Falcon 9 having 16 straight successful landings, and is about to move on to Falcon 9 having 30 planned flights next year. Then, at 8:19 in the video, he starts talking about Falcon 9 landing precision, and says, "In fact, we believe the precision at this point is good enough for propulsive landing that we do not need legs for the next version. It will literally land with so much precision it will land back on its launch mounts."

He's talking about Falcon 9. He may have misspoke since BFR was obviously on his mind, but the context says the is saying the next version of Falcon 9 can land on it's launch mounts. BFR is hardly "the next version" when discussing Falcon 9; Block V is.

I'll be the first to say that he MUST have misspoke because that is insane. The risk and additional development it would take to have Falcon 9 land its launch mounts would be insane at this stage in the booster's life. If they were planning to roll this out with Block V we would have seen a test. Also, there is no way you could land without legs on the ship due to the imprecision of the ship, and there is no way in hell that Falcon Heavy boosters could all land on their mounts.

So, it is not going to happen. Right? He misspoke right?

I think in his mind, the next version of rocket they are developing is the BFR. First version was F1, second version F9 and the "next" version is BFR. I wouldn't read too much craziness into his words.

F9 was designed to make money as an expendable, and benefit from reuse. BFR will completely depend on the economics of reuse. BFR can afford to be overly large for many payloads, because what matters is the per-flight cost, and BFR's per-flight cost will be less than F9s per-flight cost.

That means: SpaceX will make more money launching the same payload on a BFR than on a Falcon 9. Falcon 9 will vanish as soon as sufficient profitable customers have accepted BFR for their payloads.

It also means that we will see less engineering and less fabrication per flight on the BFR, in two ways that multiply together. The first is that the absolute dollar amount of engineering and fab per flight on the BFR must be less than F9, and the second is that, with larger amounts of material, many kinds of fabrication will not be economically feasible on the BFR that were feasible on F9.

The bottom line is that BFR must be managed as a more mature product than F9 has been.

My guess is that it will cost significantly less to prototype manoevering thrusters on F9 sufficient to achieve cradle recovery than to prototype legs on the BFR. Note that legs have attach points and thus load paths that do not exist on a legless vehicle. Legs also drive packaging and aerodynamics of the underlying vehicle. And finally, if you are going to risk losing a vehicle to a landing failure, it will be less expensive to lose an F9 than a BFR.

Okay, what I'm about to say is wild speculation, so bear with me, but it just dawned on me while thinking about some stuff in L2 (Just to reiterate, to the best of my knowledge, there is no info supporting what I'm about to speculate. It was just the trigger).

What if the Octagrabber was actually destined to become a testing craddle rig. Of course not in its current version. It would need to be upgraded a lot. As we've seen, it doesn't seem to support very well a fire, so much less a rocket plume.

But if it's able to hold the rocket down while at sea, I don't see why it couldn't be upgraded to grab it in the air and keep it. You can attach legs to the Octagrabber if it needs more torque capability. It's able to move around to position itself under the landing booster. Musk has mentioned that the current accuracy might be enough to allow that.

And more importantly, it would actually provide a research path towards the landing craddle technology. We've all seen the ASDSes can sustain a RUD without too much damage in case of test failure. It would provide a way to test without putting at risk any mission critical assets for other launches. The Octagrabber itself is not mission critical. So loosing it isn't that bad. Their booster production capability and reuse ramping up with block 5 on the line means it's not that bad to loose a booster here or there. There is no doubt in my mind that you prefer loosing an F9 than a BFR to test the technology.

So, what do you think ? (As I said, it sounds crazy, and maybe it is crazy. But I can't help but think it feels like the SpaceX kind of crazy ! The one we love ! )

"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY